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Tree of life
In , taxonomy is the of naming, defining ( ) and classifying groups of biological s on the basis of shared characteristics. Organisms are grouped together into (singular: taxon) and these groups are given a ; groups of a given rank can be aggregated to form a super-group of higher rank, thus creating a taxonomic hierarchy. The principal ranks in modern use are , , (division is sometimes used in botany in place of phylum), , , , , and . The Swedish botanist is regarded as the founder of the current system of taxonomy, as he developed a system known as for categorizing organisms and for naming organisms. With the advent of such fields of study as , , and , the Linnaean system has progressed to a system of modern biological classification based on the ary relationships between organisms, both living and extinct. Clade A clade (from Ancient Greek: κλάδος, klados, "branch"), also known as monophyletic group, is a group of s that consists of a and all its , and represents a single "branch" on the " ". The blue and red subgroups (below) are s, or (complete) groups; each shows its common ancestor 'stem' at the bottom of the subgroup 'branch'. The green subgroup is not a clade. It is an incomplete clade because it excludes the blue branch even though it has also descended from the common ancestor stem at the bottom of the green branch. The green box (central) could represent an , a group united by conservative anatomical and physiological traits rather than phylogeny. The green subgroup together with the blue one forms a clade again. A homoplasy is a characteristic that is shared by two or more taxa due to some cause other than common ancestry. The two main types of homoplasy are convergence (evolution of the "same" character in at least two distinct lineages) and reversion (the return to an ancestral character state). Convergent evolution From : Convergent evolution is the independent evolution of similar features in species of different lineages. Convergent evolution creates analogous structures that have similar form or function but were not present in the last common ancestor of those groups. Analogous traits arise when different species live in similar ways and/or a similar environment, and so face the same environmental factors. When occupying similar ecological niches (that is, a distinctive way of life) similar problems can lead to similar solutions. Evolution A gene that is present in only one in a million individuals and that has only a 0.1% advantage in reproduction will in only 15,000 generations be present in 75% of individuals. Traveling at 1 mm/s a snail will move 1,000 km in 31.7 years. Phylogenetic tree | label2= | 2= |1= (Rhodophyta) | 2= }} |2= | 2= (Viridiplantae) }} |3= }} | 2= |2='' '' }} |label2= |2= | label2= | 2= | 1= | 2= }} | 2= }} }} }} }} }} | 2= | label3= | 3= |label2= | 2= | label2= | 2= |1= |1= |2= a }} |label2= / |sublabel2= |2= |2= |1= }} |2= |label2= / |sublabel2= |2= |2= |2= }} }} }}}}}} }} |label2='Holozoa' |sublabel2=1100 mya |2= |2= |1= }} |label2= |2= |label2= |sublabel2=950 mya |2= |2= ia }} }}}}}}}} }} }} }} |label1= |style=font-size:80%; line-height:80%}} Integrated Taxonomic Information System *Integrated Taxonomic Information System References Category:Tree of life